This application seeks renewal of research support for five years to study the sites and mechanisms of action of psychomotor stimulant drugs, including amphetamine and cocaine. Experiments are proposed to determine the mechanisms underlying alterations in catecholaminergic and non-catecholaminergic neuronal terminal excitability, including an analysis of the influence of cocaine on catecholaminergic terminal excitability and whether changes in terminal excitability of dopaminergic neurons in the rat brain occur in the chronically implanted, behaving animal. An attempt will be made to collect converging evidence regarding the identity and postsynaptic target of dopaminergic synapses made in neostriatum and to assess the relation of dopaminergic synapses made in neostriatum to its compartmentalization into the dopaminergic islandic or striosomal and matrix compartments. Further experiments are proposed to assess the consequences of amphetamine administration on neuronal activity in neostriatal targets such as pars reticulata of substantia nigra and globus pallidus. Finally, we will continue to assess the anatomical and pathological consequences of amphetamine and cocaine administration on the rat brain using tyrosine hydroxylase immunocytochemistry, the Fink-Heimer method for identifying degeneration in caudate nucleus and cerebral cortex, and biochemical analysis of potential monoamine depletions from these sites.